This invention relates generally to rollers employed for compaction of loose material. More particularly, this invention concerns a roller having a variable amplitude vibrator.
In the past, rollers have been provided with vibrators which include a shaft having a variable position eccentric mass. In most known devices, the variable position eccentric mass may be located at two or more discrete radial positions. Generally, movement between the discrete positions can be effected only while the roller and vibrator are stopped.
Vibratory rollers of the type just described have proved to be of limited utility. For example, with discrete predetermined positions of the eccentric mass, the eccentric mass cannot be positioned intermediate the predetermined positions. Such intermediate positions are desirable when one position provides a vibration amplitude which is too great and the next adjacent position provides a vibration amplitude which is too small. These problems can occur when the vibrating roller is used to compact surface materials having different textures or having the same texture at different sites.
Another disadvantage of the known rollers is the inability to effect adjustments between the predetermined positions of the eccentric mass while the shaft carrying the eccentric mass rotates. While one known device is capable of allowing adjustment in one direction only from a maximum amplitude vibration to a minimum amplitude vibration (see U.S. Pat. No. 3,814,532), the device is basically provided with two discrete operating positions. There is no mechanism for reversing the direction of amplitude adjustment if necessary.
When compacting a material, it is often necessary to move the roller from a compacted surface region which has been treated and in which the roller has a low amplitude vibration to a different contiguous area in which the material has not yet been compacted and in which a large vibration amplitude is necessary. It is therefore desirable to be able to adjust the amplitude of vibration during operation of the machine without needing to stop the machine. Unfortunately, the known devices are not capable of providing this adjustability.
In the one known attempt to provide adjustability of vibration amplitude, a control rod is mounted to reciprocate a rotary piston carried by the shaft. Movement of the piston axially along the shaft varies, hydraulically, the position of the eccentric mass which is biased by a spring (see U.S. Pat. No. 3,059,483). Such a device, however, is limited in its usefulness since the shaft must be rotated at a frequency sufficiently low that centrifugal force of the piston does not exceed the frictional force which positions the control rod and the adjustable piston.
Other attempts at providing adjustability of the eccentric mass require the provision of one or more additional hydraulic pumps or motors in the roller which increase cost and complexity of the roller.
Another common deficiency of the known prior art resides in the inability to precisely duplicate the amplitude of the compacting vibrations at different times during operation of the roller. For example, when a portion of a surface has been finished with a vibration amplitude intermediate the maximum and minimum values and the amplitude of vibration is adjusted to another value to begin coarse compaction of a new portion of the surface, it is highly desirable to finish off the new surface portion. Thus, with an adjustable amplitude vibrator, having no discrete positions, it is highly desirable to provide means for duplicating the amplitude vibration at different times during machine operation.
In view of the foregoing, it will be apparent that the need continues to exist after a vibratory roller which is capable of infinite variations of the vibration amplitude and which is capable of duplicating a selected vibration amplitude at different times.